Direct-current (DC) to DC voltage converters are used in numerous applications to transfer power from an input DC voltage and current to an output DC voltage and current. In a typical “step-down” configuration, a voltage converter will input power from a high voltage, low current source, and output low voltage, high current power to a load of the voltage converter. In an alternate configuration, a step-up voltage converter provides, relative to its input power source, an increased voltage and decreased current to the load. Such power conversions are accomplished by generating an alternating current (AC) on the primary side of the voltage converter, passing the AC power through a transformer that steps the voltage up or down, and then rectifying the resultant AC power on the secondary side of the transformer. The rectified (DC) power is then provided to a load of the voltage converter.
A delay is associated with the transfer of power through the transformer, i.e., a voltage pulse input to a primary winding of the transformer produces a corresponding voltage pulse on a secondary winding only after some propagation delay through the transformer. The control of the voltage converter must take this delay into account, e.g., to ensure adequate “dead-time” is provided to power switches that generate the AC power on the primary side of the transformer, to control synchronous rectification switches on the secondary side of the transformer, and to track magnetic flux to prevent transformer saturation. Typically, a fixed (constant) delay is presumed, which leads to worst-case values being chosen for timing-related control parameters such as dead-time. In practice, the propagation delay through a transformer varies, and the setting of control parameters based upon a presumed constant propagation delay leads to sub-optimal performance through at least some of the operating range for the voltage converter.
Accordingly, there is a need for improved techniques for estimating the propagation delay through a transformer within a voltage converter, including techniques that account for the variation of such delay under different load conditions of the voltage converter. Furthermore, techniques for using such a load-variant delay to achieve more efficient operation of the voltage converter are needed.